1. Field of the Invention
The invention relates generally to downhole seismic sources and, more particularly, but not by way of limitation, it relates to an improved type of orbital vibration source for generating both shear wave and compression wave energy for coupling into a bore hole wall.
2. Description of the Prior Art
The prior art has seen a number of different downhole sources as used in different types of transmitter/receiver logging systems. Many different types of source mechanisms have been utilized for inducing acoustic energy into a borehole wall and subsequently analyzing velocity and/or phase of received energy to ascertain certain lithologic information. There are currently on-going efforts by a number of entities to develop suitable downhole sources for generation of shear waves and/or compressional waves which sources are capable of generating significantly greater power of energy input with high signal-to-noise ratios in order to enable certain new approaches to seismic data acquisition. Thus, current efforts take various forms and utilize diverse mechanisms in attempts to impart a clean, concise, seismic energy input through the borehole wall or, in some cases, the well casing, and it is contemplated that development of such sources will indeed open new possibilities of seismic data acquisition and interpretation.